1. Field of Invention
The present invention relates to an average current regulator, a driver circuit for an average current regulator, and a method for regulating average current. Particularly, it relates to an average current regulator which controls the ON-time of a power transistor by detecting the time point when the output current reaches an average current; it also relates to a driver circuit and a method for use in such average current regulator.
2. Description of Related Art
FIG. 1 shows a circuit diagram of a typical current regulator, in which a PWM (pulse width modulation) controller 11 controls at least one power transistor in a power stage circuit 12 to convert an input voltage Vin to an output current Iout which is supplied to a load circuit such as an LED (light emitted diode) circuit 14 shown in this figure. A feedback circuit 13 generates a feedback signal related to the output current Iout, and inputs the feedback signal to the PWM controller 11, such that the PWM controller 11 can control the power transistor in the power stage 12 to regulate the output current Iout to a predetermined target. The power stage circuit 12 may be, but is not limited to, a synchronous or asynchronous buck, boost, inverting or buck-boost converter as shown in FIGS. 2A-2I.
In the prior art, the object to be regulated is the peak current of the output current Iout, that is, the current regulator regulates the peak current of the output current Iout to the predetermined target. However, referring to the two current signals 310 and 320 shown in FIG. 3, although the peak current of the current signal 310 is the same as the current signal 320, the average current 1 of the current signal 310 is different from the average current 2 of the current signal 320. In some applications, such as in the case of FIG. 1 for controlling the LED circuit 14, this is disadvantageous because the LED circuit 14 needs a stable and well-controlled average current such that the brightness of the LEDs is uniform and stable.
U.S. Pat. No. 7,388,359 discloses an average current control circuit as shown in FIG. 4, and its mechanism of controlling the average current as shown in FIG. 5. However, in this prior art, because of the noise in the operation of the power switches, which results from the coupling of the power switches and the reverse diode current, the accuracy of the average current is not optimum.
In view of the foregoing, the present invention provides an average current regulator, a driver circuit for an average current regulator, and a method for regulating average current, to overcome the drawbacks in the prior art.